The present invention relates to systems and methods which manipulate products of web material, and more particularly, to systems and methods for stacking and separating stacks of web product.
In the various web product industries, the demand for faster product output and increased efficiency is continually increasing. Very often, a one or two-second difference in a machine cycle can greatly impact the productivity of a system or device which manipulates, packages, and/or controls the movements of web product. In many web product industries, such a difference can be determinative as to whether or not a system or device is obsolete in light of faster and more efficient alternatives. Industries in which heightened system speed is virtually always in demand include the paper (e.g., for stacking and separating tissue paper, paper toweling, napkins, etc.), foil, textile, synthetic sheeting, and other industries. Although the following discussion focuses upon apparatuses and methods for stacking and separating interfolded web paper product, it should therefore be appreciated that the same holds true for other industries such as those just mentioned and for product which may or may not be interfolded when in stacked form.
A particular design challenge exists in the quick stacking and separation of web product in, for example, interfolding equipment. Stacking and separating processes tend to be a xe2x80x9cbottleneckxe2x80x9d for upstream and downstream equipment operations. Specifically, conventional stacking and separating systems and devices typically stack a stream of interfolded product upon a stacking surface which is then either lowered, shifted, or opened to separate the stacked product thereon from a new stack of product being built. Examples of stacking surfaces can be found in U.S. Pat. No. 4,874,158 issued to Retzloff, U.S. Pat. Nos. 4,770,402 and 5,299,793 issued to Couturier, and U.S. Pat. Nos. 4,700,939, 4,717,135, and 4,721,295 issued to Hathaway, all of which disclose a stack-building surface which essentially is an-elevator floor movable between an upper stack-building position and a lower stack-discharging position. U.S. Pat. No. 4,229,134 issued to Reist teaches a stack building surface which slides to drop the built stack to a surface below. As another example, U.S. Pat. No. 4,183,704 issued to Steinhart and U.S. Pat. No. 5,730,695 issued to Hauschild et al. disclose a stack-building surface which is actually a set of fork prongs or rods extending beneath and supporting the stack as it is being built.
The process of separating a completed stack from a stack which is to be built presents a speed problem for conventional systems in that time is required to pull, drop, or shift the completed stack to downstream processes. Typically, the elements and/or assemblies necessary to perform these tasks must rapidly move between a number of positions during stacking and separation operations. Nevertheless, every such movement consumes valuable time and limits system speed. One example of wasted time evident in prior art systems is the manner in which elevator-style stack building surfaces move. Conventional systems are designed so that once the stack building surface is lowered to its stack discharging position, one or more elements must complete stack discharging operations before the stack building surface can return to its elevated stack building position. The time necessary for these operations represents an inefficiency which limits the maximum operating speed of the system.
Another problem affecting the speed of conventional stacking and separating systems arises when the systems experience a jam or misfeed. In order to control the manner in which web product is stacked upon a stacking surface, it is commonly necessary to at least partly enclose the stack building surface with rails, guides, walls, or other means. Unfortunately however, this enclosed configuration leads to significant problems during and after a misfeed or jam within the enclosed area (i.e., over the stack building surface) because the area can be very difficult to clear out. Jams and misfeeds in conventional systems are therefore very time-consuming and costly.
Yet another problem experienced in conventional stacking and separating systems is not as directly related to system speed as the problems discussed above, but nevertheless significantly impacts system operations in a negative manner. Consumer demand for stacked web product having a final fold (located at the top of the completed stack, such as for a stack of packaged tissues) creates a demand for elements and assemblies which can form a final fold on the stack during the stacking and separating process. An example of such a system is described and illustrated in the Retzloff patent mentioned above (U.S. Pat. No. 4,874,158). In the Retzloff patent, a pair of fold fingers are mounted in a set vertical position with respect to the stack of product being built. The building stack is continually lowered as it is built, until the bottom of the stack reaches a predetermined level at which are mounted the pair of fold over fingers flanking the bottom of the stack. At a controlled time, the fold over fingers slide toward and under the stack to create a final fold in the last sheet of web product. However, the fact that the fingers are mounted in one vertical position requires this folding operation to be performed at a specific time in the stack-building operation. In some cases, the folding operation therefore limits the entire stacking and separating process, and can result in system delays.
In light of the problems of prior art systems described above, a need exists for a system and method for stacking and separating stacks of web product which can separate a completed stack from a building stack and transport the completed stack to downstream operations faster than conventional systems, which can be cleared of jams and misfeeds quickly and with minimal downtime, and which can perform final folding operations in a more flexible manner to permit faster system operations. Each preferred embodiment of the present invention achieves one or more of these results.
The present invention is an apparatus and method for separating stacks of web material in a web stacking system. To accomplish this task in a faster and more efficient manner than prior art devices and systems, the invention utilizes a stack building carriage that is able to move independently of its unloading mechanism, most preferably through the use of a slotted or forked floor. The stack building carriage is mounted for movement between a stack building position in which a stack of product is built or transferred and a stack discharging position in which the stack of product is removed from the stack building carriage. The present invention also includes an unloading mechanism which can take the form of a load finger assembly which is adapted for movement through a discharge path. This discharge path passes across or beside the stack building carriage (depending upon system orientation). When the stack building carriage is located in its stack discharging position, movement of the load finger assembly through its discharge path pushes stacked product off of the stack building carriage. Preferably, the load finger assembly is provided with a number of load fingers which pass through the slotted or forked stack building carriage floor. Therefore, as the stack building carriage is moved to its stack discharging position and as the load finger assembly is moved to clear the stack from the stack building carriage, the fingers of the load finger assembly move through the slotted or forked stack building carriage floor. This permits the stack building carriage to move independently of the load finger assembly, and ensures that the two move with substantially no interference in their operations. The advantage of such a design is that after the load finger assembly has moved across the stack building carriage to clear the same, the stack building carriage can quickly return to its stack building position without waiting for the load finger assembly to return to its original position. In stacking and separating systems where a matter of a fraction of a second significantly affects product output, the time saved represents a significant advantage over conventional systems.
One highly preferred embodiment of the present invention utilizes a pair of finger assemblies flanking the path taken by the stack building carriage between the stack building position and the stack discharging position. Preferably, the finger assemblies are mounted for movement along and can be positioned in a range of locations beside the stack building carriage path. Each finger assembly preferably has a count finger, a separation finger, and a fold over element controlled by a system controller. The count fingers and separation fingers can be controlled to be inserted in a stream of web product entering the stacking and separating apparatus. In this manner, the count fingers and separation fingers cooperate to separate a completed stack of product from a new stack of product being built thereafter. Because the separation fingers are preferably mounted for movement alongside the stack building carriage path, a set of separation fingers can then be moved along with the stack building carriage away from the other set of separation fingers in order to bring the completed stack of product to the stack discharging position.
After stack discharge by the load finger assembly, the finger assemblies are preferably positioned closely below the new stack being built. Preferably, the fold over element on each finger assembly then is operated by the controller to create a final fold in the new stack of product. The fold over elements can be two fold over fingers (one on each finger assembly) cooperating to create the final fold, or can be a fold over finger and a fluid emitter such as an air jet directed to blow the tail of the new product stack around the fold over finger to create the final fold. Because the fold over elements are each preferably mounted upon the finger assemblies, the fold over elements can be moved to a number of positions along the stack building carriage path so that final fold operations can be performed in a range of desired times or at the same time for a variety of different product types and thicknesses. The various operations of the present invention therefore need not be timed, sped, or slowed to accommodate the final fold operations as is the case for prior art systems in which fold over fingers are fixed to or can only operate in one place alongside the stack building surface path.
The present invention also preferably utilizes a reject conveyor for discharging rejected stacks of product and misfed or jammed product from the system. To perform this discharging operation, the stack building carriage is preferably movable out of its normal path (between the stack building and stack discharging positions), and the load finger assembly is retracted. An unobstructed path is thereby cleared through the system for rejected, misfed, or jammed product to pass through to the reject conveyor. This reject feature prevents undesirable product stacks from proceeding to downstream operations, and saves considerable time compared to prior art systems which typically require stack building areas within the system to be manually cleared in the event of a misfeed or jam.
More information and a better understanding of the present invention can be achieved by reference to the following drawings and detailed description.